DIY Audio Projects Forum

Welcome to the DIY Audio Projects Message Forum. Use these forums to discuss Hi-Fi audio and to share your DIY Audio Projects. Registration is free and required to post messages and view the file attachments. Registration will only take a minute and registered users do not see any advertisements. After you have completed the online registration process, check your email (including spam/junk folder) for the verification email to activate your account. New members are under moderation - so your posts will not be visible until approved by a moderator. See the Read Me 1st, Forum RULES and Forum FAQ to get started on the forum.

Bruce & Team,The latest findings. Sorry to say that:1) grounding to the signal grounds the metal cases of the coupling caps did not make a difference,2) placing a short between the grid of the lower triode section of the driver stage and ground, did not make a difference also. The noise is still there and at the same level.

Hi, Hummm. What I would like you to do is describe exactly (as possible ) what is still going on as I have lost track of all the things we have tried and we should start to trouble shoot from the basics. Clearly we are missing something. Additionally please tell us about the set up / configuration and everything that is connected to it. I don't know about anyone else, but I have lost track of what has been tried and what happened. I appologize for that, but with four fourms, 5 email accounts, a business web site and bunches of individual inquiries I sometimes get lost. BTW, where do you live? There may be a forum member that is nearby and can assist.

Maybe contradicting with the previous message:- taking out the driver tube eliminates the noise;- switching off the block (working just on the capacitors charge) eliminates the noise;- blocking input signal (grounding input RCA or the lower tube grid) does not help;- grounding FT-3 capacitors does not cure the problem;- changing ground layout does not help also.What may I suggest to try: remove the LR8 and replace it with a resistor (the value of the resistor can be estimated from the previous versions of the power secion of the driver tube or just measuring the voltage between in and out of LR8 and count).

What may I suggest to try: remove the LR8 and replace it with a resistor (the value of the resistor can be estimated from the previous versions of the power section of the driver tube or just measuring the voltage between in and out of LR8 and count).

Poty,

OK. Thanks.See the before and after figures. I want to make sure I get it right. Is this what you are suggesting to do?What are you trying to determine? If the LR8 is introducing oscillations?What do you mean by "count" in "measuring the voltage between in and out of LR8 and count".

Bruce,

I live in NJ.

Thanks,

Danny

This post has a file attachment. Please login or register to access it. Only Registered Members may view attached files.

I've been following this thread and the troubleshooting steps. The one thing that stood out for me was that the noise disappeared immediately when Danny switched off the AC power. The audio continued, noise-free, until the capacitors discharged. Switching off the AC removed whatever ripple content that remains in the rectified and filtered DC. Is it possible that the 120 hz ripple could be exciting some weird oscillation in the LR8? Maybe just a freak thing with just the right amount of capacitance around the LR8? I don't know if that is even possible, but....The test that Poty suggested, removing the LR8 from the circuit will be interesting....

See the before and after figures. I want to make sure I get it right. Is this what you are suggesting to do?

Yes, but if you have a capacitor on hand (voltage - more than 350V, capacitance 40-100uF) please put it across the 0.22uF. I also doubt you'll have to remove 910R/220k divider

Danny wrote:

What are you trying to determine? If the LR8 is introducing oscillations?

Any weird thing with LR8. As Jim_O already mentioned - all the experiments points to the power supply circuit.

Danny wrote:

What do you mean by "count" in "measuring the voltage between in and out of LR8 and count".

Sorry, my English is far from perfect. There is a voltage which is dropped on LR8 (let's call it Vio). There is a current for driver part (Id = 1mA for SRPP + 1.3mA for 910/220k divider + 1mA for heaters' lifting). You can use the Ohm law to count the resistor with the same voltage drop: R=Vio/Id. Alternatively you can determine Id just by measuring the voltage across the 33k resistor (Vr): Id=Vr/33k.

Well, I am happy to finally report that my white noise/hiss problem has been resolved.As suggested by poty, I replaced the LR8 circuitry with a 33K resistor in series and an additional 47uF cap in parallel and the amp is now dead quiet. I can finally rest...and enjoy the music.I don’t have the proper equipment to fully analyze this issue. So, I leave it to you, the experts, to discuss why the LR8 would cause this. Oscillations issues?

Also, I while ago I reported that I had a problem where the voltage across the test points at start up would hover up to 240mV for several minutes and then settled to the correct setting of 92 mV.On further investigation it turns out that it would do this routinely and not just at start up. Anyway, I thought that I had solved the problem by removing a terminal block that I was using to connect the LM317 to the mother board. But, this was incorrect. The problem was sporadic in nature. Thus, difficult to observe. Finally in desperation I replaced the LM317 and the problem went away. Thus, LM317 can also fail in this peculiar fashion. Where they work sometimes and sometimes they decide to go crazy.

Thanks to all for the support. Especially poty and Bruce. Now, I need to go and replace the LR8 on the second monoblock.Thanks to all,

Hi, I kind of wonder if you were sold either seconds or bogus parts. I have probably personally used 100 of each type and never had a problem that was not caused by some "oops" on my part. In the comercial kits they are virtually never at fault for an issue (except for someone elses oops). Having several go "bad" in your builds is extremely unusual. Most curious.

Hi, I have used their parts often and never had a problem. The LR8 is slightly sensitive to static, but not like a CMOS chip. I don't handle them with a lot of care. They will fail if improperly connected or shorted. I have never seen a noisy one or one that oscillated if used correctly. The LM317 is nearly bullet proof. I don't think you can harm one easily. Over votlage is the only way I have found. Even then they will usually put up with votlages about twice the rating and survive fine. If you over heat them they can fail though. Your problems and findings are very strange. That is why they took so long to discover. Things that don't normally behave that way are not generally suspected as cause factors. Maybe they got some duds.

Who is online

Users browsing this forum: Google [Bot] and 14 guests

You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum